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Subscriber access provided by CARNEGIE MELLON UNIV Article Response Surface Optimization of Impregnation of Blended Amines into Mesoporous Silica for High-Performance CO Capture Duc Sy Dao, Hidetaka Yamada, and Katsunori Yogo Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 22 Jan 2015 Downloaded from http://pubs.acs.org on January 26, 2015 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication They are posted online prior to technical editing, formatting for publication and author proofing The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record They are accessible to all readers and citable by 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realm Crown government in the course of their duties Page of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels Response Surface Optimization of Impregnation of Blended Amines into Mesoporous Silica for HighPerformance CO2 Capture Duc Sy Dao,†,‡ Hidetaka Yamada,§ and Katsunori Yogo*,†,§ † Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan ‡ Faculty of Chemistry, Hanoi University of Science, VNU, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam § Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan *To whom correspondence should be addressed Tel: +81-774-75-2305; Fax: +81-774-75-2318 E-mail: yogo@rite.or.jp (K Yogo) ABSTRACT: We used the response surface method (RSM) to optimize the conditions for the impregnation of blended amines into mesostructured cellular silica foam (MSU-F) to prepare effective solid sorbents for CO2 capture The effects of the amounts of tetraethylenepentamine (TEPA), diethanolamine (DEA), and MeOH in the wet impregnation mixture on the amounts of CO2 adsorbed were investigated The influences of these three independent variables and their interactions were determined using the RSM; the optimum amounts of TEPA, DEA, and MeOH were 1.33 g (7.03 mmol), 0.85 g (8.08 mmol), and 58.2 g, for the preparation of g of sorbent Under the adsorption conditions 40 C and 100 kPa CO2, the optimum sorbent showed fast kinetics and an excellent CO adsorption of 5.64 mmol/g; the value predicted by the RSM model was 5.67 mmol/g Analysis of variance and the coefficient of determination (R2 = 0.9525) showed the utility of the approach used in this study to optimize the conditions for preparing high-performance solid sorbents For the optimum sorbent, the ACS Paragon Plus Environment Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page of 28 heat of adsorption was determined to be 78.9 kJ/mol CO2 at 40 C and 100 kPa, using a Calvet calorimeter, indicating relatively strong chemisorption in the form of carbamate We also found that the amounts of CO2 adsorbed by the optimum sorbent depended substantially on the adsorption temperature The highest CO2 adsorption, 6.86 mmol/g, was obtained at 50 °C and 100 kPa INTRODUCTION The atmospheric concentration of CO2, which is a primary greenhouse gas, is increasing, mainly because of anthropogenic activities such as fossil fuel combustion To mitigate this problem, CO2 emissions need to be reduced significantly from their current level It is widely believed that the CO2 capture and storage (CCS) method is viable option in this context.1–6 However, one of the critical issues in CCS deployment is reducing the energy costs, especially in the capture process High-performance materials for CO2 capture have therefore been extensively explored and studied in recent years One promising method for CO2 capture is the use of solid amine sorbents, which have the following advantages: (i) low energy requirements for sorbent regeneration because of the absence of solvents, (ii) potentially high adsorption capacity because of the dense amine-containing structure, and (iii) the low corrosion and toxicity caused by amines anchored to solid supports.7–12 Solid amine sorbents can be prepared by the wet impregnation of liquid organic amines into porous supports or the covalent grafting of amines onto porous surfaces using silane coupling agents.3,4,11,13 Wet impregnation is a simple preparation method, by which a large amount of amine can be introduced into the pores of the support, leading to a higher CO2 adsorption capacity compared with those of sorbents prepared using grafting methods Mesoporous silica materials, including hexagonal MCM-41,4,14–16 SBA-12,13 SBA-15,13,14 twodimensional hexagonally ordered MSU-H,4 and mesocellular silica foam MSU-F4 have been used for amine loading because of their high surface areas and thermal stabilities MSU-F, which has large pore volumes, large pore sizes, and good pore interconnections, showed high CO2 adsorption performance ACS Paragon Plus Environment Page of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels after wet impregnation of amines.4 The amines can be linear or branched polyamines such as tetraethylenepentamine (TEPA) or polyethyleneimine (PEI), which have been impregnated into mesoporous materials to attain high-contents of reactive sites, i.e., amino functional groups.3–5,8,10–12,17 Recently, we reported the development of solid sorbents using several mesoporous silica materials prepared by wet impregnation of amines and organic compounds with/without hydroxyl groups.4 The results showed that in addition to large mesopores, hydroxyl groups have positive effects on the amounts of CO2 adsorbed Consequently, new sorbents with high performances in CO2 adsorption have been developed using large-pored MSU-F silica and polyamine/alkanolamine blends Among some amine blends, TEPA/diethanolamine (DEA) was the most effective The results also indicated that the molar ratio of amino to hydroxyl groups is a key determinant of the adsorption performance and, depending on this ratio, the amine blends showed synergistic effects with regard to the amount adsorbed In this study, we determined the optimum conditions for the preparation of solid amine sorbents with high CO2 adsorption performances, and evaluated the effects of, and interactions among, the variables in sorbent preparation For the development of an acceptable process in the shortest time using the minimum number of experiments, time, and materials, we used the response surface method (RSM), which is a powerful mathematical and statistical technique for the investigation of various processes and can be widely used for designing experiments, building models, process modeling and optimization.18,19 A few applications of the RSM to the optimization of processes for CO2 capture by solid sorbents have been reported.19–21 Shafeeyan et al.19 developed models for calculating the optimum conditions for amination of activated carbon for the preparation of CO2 sorbents by investigating the effects of amination temperature and time on the CO2 adsorption/desorption performance Gil et al 20 used the RSM as a tool for rapidly optimizing activation parameters such as activation temperature and burn-off degree to obtain the highest CO2 adsorption capacity of activated carbon Aziz et al.21 used a ACS Paragon Plus Environment Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page of 28 fractional factorial design to functionalize mesoporous silica particles with aminopropyltriethoxysilane and showed that the amount of water present during synthesis, the reaction time, pretreatment of the silica with a mineral acid, and certain two-way interactions were important in the optimization of CO2 uptake The main aim of this study was optimization of the conditions for the impregnation of MSU-F with a mixture of TEPA and DEA for high-performance CO2 capture We used the RSM to investigate the effects of the amounts of TEPA, DEA, and solvent (MeOH), and their interactions, on the amounts of CO2 adsorbed For the optimum sorbent, prepared based on the model developed using the RSM, we evaluated the amount of CO2 adsorbed and its temperature dependence We also measured the heat of adsorption using an isothermal calorimetric method EXPERIMENTAL SECTION 2.1 Materials All chemicals were purchased and used without further purification TEPA [98%, H(NHCH2CH2)4NH2] and MSU-F were purchased from Sigma-Aldrich (St Louis, MO, USA) DEA [99%, (HOCH2CH2)2NH)] and MeOH (99.8%, CH3OH) were supplied by Wako (Osaka, Japan) He (99.9999%) and N2 (99.9999%) gases were purchased from the Iwatani Gas Company (Osaka, Japan) CO2 (99.995%) was provided by Sumitomo Seika Chemicals (Osaka, Japan) 2.2 Preparation of Solid Sorbents Amine-functionalized MSU-F sorbents were prepared using the wet impregnation method A specific amount of MSU-F was added to MeOH and the mixture was agitated ultrasonically for The required amounts of TEPA and DEA were then added and the mixture was agitated for The solid sorbents were obtained by MeOH removal with a rotary evaporator at 60 °C The prepared sorbents were denoted by TEPAx1-DEAx2/MSU-F/x3, where x1 and x2 represent the mass fractions of TEPA and DEA, respectively, and x3 represents the mass of MeOH used in the preparation of g of sorbent; for example, TEPA40-DEA30/MSU-F/75 represents the sorbent prepared by loading a mixture of 1.2 g (40 wt%) of TEPA and 0.9 g (30 wt%) of DEA into the pores of ACS Paragon Plus Environment Page of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels MSU-F (0.9 g, 30 wt%) with 75 g of MeOH 2.3 Material Characterization N2 adsorption–desorption isotherms were obtained using a surface area and porosimetry measurement system (ASAP 2420, Micromeritics, Norcross, GA, USA) Preadsorbed water and CO2 were removed by degasification at 40 C under a N2 flow for h before the adsorption–desorption analysis To improve the data integrity, all the experiments, including measurements of CO2 adsorption isotherms, were set up with adequate equilibration intervals; filler rods were used to ensure sample accuracy by reducing the free-space volume Equilibration was reached when the pressure change per equilibration time interval was less than 0.01 of the average pressure during the interval The specific surface areas of the materials were calculated using the Brunauer– Emmett–Teller (BET) method The total pore volume was determined as the volume of liquid N2 adsorbed at a relative pressure of 0.97 The pore size was determined by the Barrett–Joyner–Halenda method using the adsorption branch Thermogravimetric (TG) curves were obtained, using a Thermo Plus TG-DTA 8120 analyzer (Rigaku, Tokyo, Japan), in He gas at a flow rate of 300 cm3/min For TG analysis, the samples (mass about 10 mg) were heated from approximately 30 to 1000 °C at a constant rate of °C/min Elemental analysis was performed using an elemental analyzer (Perkin Elmer 2400II CHNS/O, Waltham, MA, USA) The heat of adsorption was measured using a Calvet C80 calorimeter (SETARAM Instrumentation, Caluire, France) The sorbent (about 200 g) was activated at 80 °C for h under N2 at a flow rate of 50 cm3/min The sample was cooled to 40 °C, and then CO2 was passed through the sample at a rate of 45 cm3/min at atmospheric pressure The heat of adsorption at 40 °C and 100 kPa CO2 was determined based on the measured value of the total heat and the adsorption isotherm 2.4 Sorption Studies The amounts of CO2 adsorbed were measured at 40 C up to a pressure of 100 kPa, using an ASAP 2020 instrument (Micromeritics) The amount of CO2 adsorbed at 40 C and 100 kPa was used as the dependent variable in the optimization For investigating the effects of temperature on the amounts of CO2 adsorbed, pure adsorption isotherms at different temperatures were ACS Paragon Plus Environment Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page of 28 measured using an ASAP 2020 instrument (Micromeritics) or a chemical adsorption analyzer (ChemiSorb HTP, Micromeritics) in the adsorption temperature range from 20–80 °C Before the adsorption–desorption measurements, degassing was performed at the adsorption temperature for h under vacuum to remove any preadsorbed moisture and gas The pure CO2 adsorption kinetics was evaluated gravimetrically at 40 °C and atmospheric pressure using a Thermo Plus TG-DTA 8120 instrument (Rigaku) The sample (about 10 mg) was placed in a Pt pan The sorbent was pretreated at 80 °C in N2 at a flow rate of 100 cm3/min for h, and then cooled to 40 °C The N2 flow was then switched to CO2 at a flow rate of 70 mL/min for h RESPONSE SURFACE OPTIMIZATION The optimum conditions for the preparation of solid sorbents for high-performance CO2 adsorption were determined by the RSM using Modde software (Umetrics, Umeå, Sweden) In this study, sorbent preparation was performed based on factorially designed experiments The amounts of TEPA, DEA, and MeOH were chosen as three independent variables, and their effects on the amounts of CO2 adsorbed were examined The experiments were conducted using the central composite design (CCD) method, with three center points, and fitted to an empirical full second-order polynomial model Table shows the ranges and levels of independent variables used in this study; low, center, and high levels are denoted by –1, 0, and +1, respectively This design also required experiments to enable prediction of the responses outside the cubic domain, denoted by –1.682 and +1.682 The RSM model was constructed by fitting the experimental data for the amounts of CO2 adsorbed with the following equation: Y o i X i ii X i2 ij X i X j i i i (1) j where Y represents the response, i.e., the amount of CO2 adsorbed at 40 C and 100 kPa, o is a constant, i , ii , ij are the linear, quadratic, and interaction term coefficients, respectively, X i is the ACS Paragon Plus Environment Page of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels coded value of the ith independent variable, and is the random error These coded values can be determined according to the following equation: Xi xactual xhigh xlow xhigh xlow (2) where xactual, xhigh, and xlow are the real values of the ith independent variable under the operating conditions, and at the high level and low level, respectively RESULTS AND DICUSSION 4.1 Material Characterization The textural parameters of MSU-F and all the sorbents were determined using N2 adsorption–desorption isotherms Figure shows the N2 adsorption–desorption isotherm and pore size distribution (inset) for MSU-F; values of 272 m2/g, 1.54 cm3/g, and 28 nm were obtained for the surface area, total pore volume, and pore diameter, respectively Table shows the complete design matrix used for the preparation of all 17 sorbents with the corresponding results for the textural properties and amounts of CO2 adsorbed at 40 °C and 100 kPa After the amines were loaded into the support, the BET surface areas and total pore volumes of all the samples decreased from 272 m2/g and 1.54 cm3/g to less than 30 m2/g and 0.2 cm3/g depend on the amine loading, respectively, indicating that the support pores were filled with the amines The thermal properties of the materials were determined using TG analysis The silica support showed good thermal stability, and only approximately wt% was lost, because of moisture The TG data also confirmed that the amines used for sorbent preparation were completely loaded into the MSUF pores Examples of the TG data are shown in Figure The samples began to lose about 610% of their weight below 100 °C; this can be attributed to preadsorbed gases and solvent that could not be completely removed The weight of the remaining solids after thermal analysis confirmed that the amines used for wet impregnation were completely loaded into the pores ACS Paragon Plus Environment Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page of 28 4.2 RSM Model The effects of the operating parameters for the preparation of the solid sorbent on the amount of CO2 adsorbed were investigated using the RSM CCD-designed experiments were performed to visualize the effects of the independent factors on the response As shown in Table 2, the amount of CO2 adsorbed varied from 3.85 to 5.63 mmol/g, depending mainly on the effects of the concentration and composition of the amine blend;4 the amine efficiency, which was defined as the molar ratio of CO2/N, was in the range 0.27–0.50 The effects of the three variables were evaluated from the experimental results in Table 2, and the following approximate response function was obtained: Y = 5.62192 + 0.0830368X1 – 0.0345798X2 – 0.0208987X3 – 0.156328X12 – 0.619369X22 – 0.140422X32 – 0.295X1X2 – 0.215X1X3 – 0.1375X2X3 (3) where Y is the amount of CO2 adsorbed at 40 °C and 100 kPa, and X1, X2, and X3 are the coded values of the doses of TEPA, DEA, and MeOH, respectively Figure shows the relationship between the values predicted using eq and the experimental values for the amount of CO2 adsorbed at 40 °C and 100 kPa The fit with the model represented by eq was evaluated based on analysis of variance (ANOVA) and the coefficient of determination (R2) The ANOVA results for the empirical second-order polynomial model are shown in Table The F-value of 15.6045 indicates that the developed model is highly significant Furthermore, the p value of 0.001, which is lower than 0.05, suggests that the model is statistically significant 21,22 The R2 value of 0.9525 means that 95.25% of the response variability is explained by the model and also confirms that the model has good predictability, for which at least R2 = 0.80 is suggested.23 The reproducibility was determined to be 0.998, using Modde software; this confirms the good predictability of the model 24 4.3 Effects of Independent Variables and Analysis of Response Surface The RSM model developed in this study was used to study the effects of the TEPA, DEA, and MeOH doses on the amount of CO2 adsorbed; the results are shown in Figure 4a, 4b, and 4c, respectively In the figure, each ACS Paragon Plus Environment Page of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels factor is varied from a low to a high level, while the other two factors are kept at the center level Figure 4a shows that the amount of CO2 adsorbed increased from 5.04 to 5.64 mmol/g with TEPA doses from 32 to 40 wt% However, when the TEPA dose increased from 40 to 48 wt%, the response decreased to 5.33 mmol/g Similar results were obtained for the effect of the DEA dose, as shown in Figure 4b The effect of the MeOH dose was small compared with those of the TEPA and DEA doses (Figure 4c) This result indicates that amines are dispersed well into the pores of supports by MeOH and suggests the robustness of the RSM model in this study The regression coefficients in eq for X1, X2, X3, X12, X22, and X32, confirm that the doses of TEPA (X1) and DEA (X2) had greater effects on the response than did the MeOH dose (X3) The absolute values of the coefficients were largest for X1 and X22, for the linear and quadratic terms, respectively These results suggest that chemisorption by TEPA and DEA strongly contributes to the CO2 uptake; this can be represented by the following equations: H(NHCH2CH2)4NH2 + CO2 H+[H(NHCH2CH2)4]NHCOO (4) 2(HOCH2CH2)2NH + CO2 (HOCH2CH2)2NH2+ + (HOCH2CH2)2NCOO (5) In our previous study,4 TEPA70/MSU-F/100 and DEA70/MSU-F/100 showed amine efficiencies of 0.23 and 0.51, respectively These values suggest that only one amino group in a TEPA molecule forms a carbamate as in eq 4., while the amine efficiency of DEA can be explained by the stoichiometry of carbamate formation shown in eq 5.25,26 Although DEA has the lower amine density than TEPA, it’s amine efficiency is higher than TEPA This is because in DEA, instead of the amino group, the hydroxyl group can play a role in stabilizing the carbamate anion.4 In the present case, as stated above, the amine efficiency for TEPAx1-DEAx2/MSU-F/x3 lies between these two limiting values (Table 2) The coefficient in eq for the X1X2 term is also significant, as it indicates interaction between TEPA and DEA; this is partly ascribed to the effect of hydroxyl groups.4 The contour and three-dimensional plots in Figure 5a and 5b show the effects of TEPA and DEA doses on the amount of CO2 adsorbed, with the MeOH dose kept at the center level As can be seen from these figures, the optimum region is for doses of TEPA and DEA of 4244 and 2830 wt%, ACS Paragon Plus Environment Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 14 of 28 Zhang, X.; Zheng, X.; Zhang, S.; Zhao, B.; Wu, W Ind Eng Chem Res 2012, 51, 15163–15169 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Chuang, S S C.; Soong, Y.; Gray, M Energy Fuels 2006, 20, 1514–1520 37 Rezaei, F.; Jones, C W Ind Eng Chem Res 2013, 52, 12192–12201 38 Fujiki, J.; Yogo, K Energy Fuels 2014, 28, 6467–6474 ACS Paragon Plus Environment 16 Page 17 of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels Figure Captions Figure N2 adsorption–desorption isotherm and pore size distribution of MSU-F Figure Typical TG curves for MSU-F before and after amine loading Figure Experimental values plotted against predicted values for amounts of CO2 adsorbed Figure Effects of TEPA dose (a), DEA dose (b), and MeOH dose (c) on amount of CO2 adsorbed, with 95% confidence intervals Effects are for variation of factor from a low to a high level, with all other factors kept at center level Figure Contour and three-dimensional response surface plots for amounts of CO2 adsorbed Figure Pure CO2 adsorption kinetics (a) and heat of adsorption (b) of optimum sorbent at 40 °C and atmospheric pressure Figure CO2 adsorption isotherms for optimum sorbent at different temperatures under CO2 pressure up to 100 kPa (a) and 15 kPa (b) ACS Paragon Plus Environment 17 Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 18 of 28 Table Parameters in CCD Statistical Experimenta coded variable levelb variable TEPA DEA MeOH a symbol X1 X2 X3 unit 1.682 1 +1 +1.682 wt% 31.59 35 40 45 48.41 (mmol/g) (1.669) (1.8) (2.1) (2.4) (2.557) wt% 13.18 20 30 40 46.82 (mmol/g) (1.253) (1.9) (2.9) (3.8) (4.453) g 32.95 50 75 100 117.05 For the preparation of g of sorbent bThe low, center, and high levels are denoted by –1, 0, and +1, respectively ACS Paragon Plus Environment 18 Page 19 of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels Table Response Surface Design and Experimental Results no coded variable levels TEPA DEA MeOH SABETa (m2/g) Vporeb (cm3/g) N contentc (mmol N/g) efficiency adsorbed (mol amount (mmol CO2/g)d CO2/mol N) 4.16 0.41 1 1 1 21.32 0.125 10.05 1 1 4.99 0.011 12.52 5.03 0.40 1 1 1.59 0.001 11.86 4.65 0.39 1 1 1.69 0.003 14.11 4.98 0.35 1 1 25.39 0.164 9.50 4.44 0.47 1 4.06 0.011 12.47 5.09 0.41 1 1 2.38 0.005 11.54 5.02 0.43 1 0.85 0.002 14.09 3.85 0.27 1.682 0 15.64 0.088 10.19 5.12 0.50 10 1.682 0 2.99 0.004 14.16 5.39 0.38 11 1.682 26.99 0.192 10.31 4.02 0.39 12 1.682 0.85 0.001 14.21 3.87 0.27 13 0 1.682 4.57 0.008 12.20 5.26 0.43 14 0 1.682 5.50 0.010 12.23 5.34 0.44 15 0 3.73 0.005 11.96 5.61 0.47 16 0 3.12 0.004 11.20 5.63 0.50 17 0 3.30 0.004 11.46 5.59 0.49 a The surface area was calculated using the BET equation in the relative pressure range 0.03–0.1 bThe pore volume was calculated from N2 adsorption isotherm data at a relative pressure of 0.97 cThe nitrogen content was determined by elemental analysis dMeasured at 40 °C and 100 kPa ACS Paragon Plus Environment 19 Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 20 of 28 Table ANOVA Results for Response Surface Quadratic Model DFa SSb MSc (variance) total 17 411.791 24.223 constant 405.821 405.821 total corrected 16 5.96942 0.373089 regression 5.68601 0.631779 residual 0.28341 0.0404871 lack of fit 0.282143 0.0564286 pure error 0.00126664 0.000633322 a Fd pe SDf 0.611081 15.6045 0.001 0.794845 0.201214 89.0993 0.011 0.237547 0.0251659 Degree of freedom bSum of squares cMean squared value dF-distribution value ep-value f Standard deviation ACS Paragon Plus Environment 20 Page 21 of 28 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels Table Properties of Solid Sorbent Prepared under Optimum Conditions optimum conditiona a textural property CO2 adsorbed amount TEPA DEA MeOH surface area pore volume predicted Experimental error (wt%) (wt%) (g) (m2/g) (cm3/g) (mmol/g) (mmol/g) (%) 44.4b 28.4c 58.2 2.43 0.003 5.67 5.64d 0.53 For the preparation of g of sorbent b2.35 mmol/g c2.70 mmol/g dAverage of three repeated experiments for separately prepared sorbents: 5.56, 5.67, and 5.69 mmol/g at 40 °C and 100 kPa ACS Paragon Plus Environment 21 Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 22 of 28 Figure ACS Paragon Plus Environment Page 23 of 28 MSU-F 100 80 Weight (%) 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels TEPA35-DEA20/MSU-F-50 TEPA45-DEA20/MSU-F-50 60 TEPA40-DEA30/MSU-F-75 40 20 25 225 425 625 825 1025 Temperature (oC) Figure ACS Paragon Plus Environment Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 24 of 28 Figure ACS Paragon Plus Environment Page 25 of 28 Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Figure ACS Paragon Plus Environment Energy & Fuels 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 26 of 28 Figure ACS Paragon Plus Environment Page 27 of 28 CO2 adsorption amount (mmol/g) (a) 0 20 40 60 80 Time (min) 100 120 180 160 140 Heat flow (mW) 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Energy & Fuels 120 100 80 60 40 20 (b) 0 20 40 60 80 Time (min) 100 120 Figure ACS Paragon Plus Environment Energy & Fuels (a) CO2 adsorption amount (mmol/g) 20 ºC 30 ºC 40 ºC 60 ºC 70 ºC 80 ºC 50 ºC 0 20 40 60 80 100 CO2 pressure (kPa) (b) CO2 adsorption amount (mmol/g) 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 28 of 28 20 ºC 50 ºC 80 ºC 30 ºC 60 ºC 40 ºC 70 ºC 0 12 15 CO2 pressure (kPa) Figure ACS Paragon Plus Environment ... Surface Optimization of Impregnation of Blended Amines into Mesoporous Silica for HighPerformance CO2 Capture Duc Sy Dao,†,‡ Hidetaka Yamada,§ and Katsunori Yogo*,†,§ † Graduate School of Materials... was pretreated at 80 °C in N2 at a flow rate of 100 cm3/min for h, and then cooled to 40 °C The N2 flow was then switched to CO2 at a flow rate of 70 mL/min for h RESPONSE SURFACE OPTIMIZATION The... the response surface method (RSM) to optimize the conditions for the impregnation of blended amines into mesostructured cellular silica foam (MSU-F) to prepare effective solid sorbents for CO2 capture